Meetup in Clojure

Calculate the date of meetups.

Meetup

Typically meetups happen on the same day of the week. In this exercise, you will take
a description of a meetup date, and return the actual meetup date.

Examples of general descriptions are:

the first Monday of January 2017

the third Tuesday of January 2017

the Wednesteenth of January 2017

the last Thursday of January 2017

Note that "Monteenth", "Tuesteenth", etc are all made up words. There
was a meetup whose members realized that there are exactly 7 numbered days in a month that
end in '-teenth'. Therefore, one is guaranteed that each day of the week
(Monday, Tuesday, ...) will have exactly one date that is named with '-teenth'
in every month.

Given examples of a meetup dates, each containing a month, day, year, and descriptor
(first, second, teenth, etc), calculate the date of the actual meetup.
For example, if given "First Monday of January 2017", the correct meetup date is 2017/1/2